Pickling liquor and process



, tension in Patented Jan. 27, 1925.

1,524,435 PATENT OFFICE.

ADDISON I. HOFFMAN AN D WILLIAM M. PARKIN, OF PITTSBURGH, PENNSYLVANIA.

rrcx nme Lrouon AND rnocnss.

in Drawing.

To all whom it may concern:

Be it known that we, AnnIsoN F. Horr- MAN and WILLIAM M. PARKIN, both citizens of the United States, residing at Pittsburgh, in the count of Allegheny and State of Pennsylvania, have invented new and useful Improvements in Pickling Liquors and Processes, of which the following is a specification.

The present invention relates to improvements in pickling metals, and constitutes an improvement on Patent No. 1,221,735 issued to Hoffman and Parkin.

In the process of said prior patent, sulfite waste liquor such as is left when wood or similar material. is boiled with a solution of calcium bisulfite or calcium sulfite in sulphurous acid, is first neutralized'with an alkali such as lime, is then concentrated to the form of a thick syrupy mass or even to dryness and some of the concentrated material is then added to the acid pickle liquor used in pickling ferrous metal articles, such as a cast iron or steel, to remove the surface rust or scale therefrom, to leave a clean metal surface. After extensive research, we have now found that the neutralization of the waste sulfite liquor before evaporation is an unnecessary and undesirable step, for the reason that the sulfite waste liquor when concentrated, preferably in vacuo, without the addition thereto of lime, soda or other alkali, is far superior for use with the pickle liquor.

It is well known that in the pickling of ferrous metal articles a usually evolved hydrogen gas, carrying therewith a relatively small amount of droplets of the acid solution, in the form of a mist of fine. particles, frequently referred to in the, trade as fume. This fume is more or less injurious to the health of the workmen and is uncomfortable and hence causes a lowering of theefiiciency of the workmen, andalso it does considerable damage to buildings and to metallic products 1n the vicinity of the pickling vats. It is well known that mist containing acid, striking iron articles leaves the same in a condition in which they will ra idly rust and corrode. The concentrated su fite waste liquor of the prior patent referred to was added for roducing more or less surface the pickling solution, so that the escapin hydro would be filtered or cleanse from mist of liquid particles.

' contains a or like material with acid, there is,

Application filed January 22, 1923. Serial No, 614,316.

By the use of the sulfite liquor concentrated without the addition of lime or other alkali, a more persistent foam is produced on the pickling bath from the same amount of the concentrated sulfite'liquor, and the foam also acts as an insulator to prevent loss of heat from the bath, reducing the amount of fog in the winter time in the pickling house. Where the acid gas dissolved in water, such as hydrochloric acid, the foam blanket holds the gasin solution, preventing loss of hydrochloric acid gas. Both of these effects are produced in a greater degree, by the use of sulfite waste liquor which has been concenthereby greatly i trated without the addition of alkali, especially lime, before the concentration. This concentrated product will hereinafter be referred to as acid concentrated sulfite waste liquor.

comes. from the digestors in which wood has been digested, is first filtered or otherwise treated to separate insoluble foreign materials from the liquor. It is then run without any chemical treatment into a concentrating pan in which it is concentrated preferably in vacuo and out of contact with air. This concentration can be carried to any desired degree, for

In the preferred mode of operation of example, a thick syrup having a gravity of about 30 to 32 B., can be produced, or the liquid can, if desired, be evaporated to dryness. The waste liquor, treated as above referred to, contains very little free sulphurous acid, since this escapes mostly durmg the concentration operation. During the cooking operation a considerable proportion of the sulfites may have been converted into sulphates. During the concencentration therefmay be more or less precipitation and the precipitate can be removed from the hot liquor by filtration, at any stage of the concentration 0 eration.

The pickling of ferrous meta articles in acid pickle containing the neutralized and concentrated sulfite liquor sometimes produces a black skin or coating on the metal articles, whereas the acid-concentrated material does not produce this effect. The acid-concentrated material. ismore effective, the same amount producing a greater increase in surface tension and hence a thicker lvzaygar of the foam on the pickling bath.

ile both the acid-concentrated material I 3 are substantially neutral to some of the indicators, it found that the neutralizedconcentrated liquor when added to the the of acid to the bath, in order to have the same acidity of the bath for pickling purposes. The acid-concentrated sulphite liquor when added to the picklingbath seems to act to revent to some extent at least, action of t e acid of the bath, on the clean metal surface, whereby the operation of the pickling is largely confined to the scale or rust on the ferrous metal articles under treatment. This causes a reduction in the amount of loss of weight of the ferrous metal articles.

l-Ieretofore it has. been well known that a portion of the hydrogen formed by the action of the acid on the metal was absorbed by the metal, andthis has to be removed by an annealin treatment after the pickling operation. The absorption of hydrogen by the metal produces more or less brittleness in the ferrous metal article. If the annealing were to be omitted, the subsequent escape of the absorbed hydrogen maycause the flaking ofi of the coatmg of the ferrous metalarticles thus for instance, blisters on enameled ware, are frequentl caused b not completely driving ofi a orbed hy rogen taken: up by the tal durin the pick 7 operation. The of 'ac i 'concentra i g sul hite waste liquor seems to prevent, to a ar e extent at least, the absorption. of the during the ic operation. effect of the a rption of hydrogen-by the ferrous metal articles being pickled is a decrease in the strength thereof. For example, it was noted that steel bars breakydro n ing at 80,000 pounds before pickling broke by t e at 60,000 unds after pickling ordinary me od, but in cases where theacidconcentrated sulfite liquor was added to the ickling bath, there was no appreciable itlerence between the breaking strength on the pickled and unpickled bars. In cases where the small amount of hydrogen absorbed in the resence of acid-conoent sulfite liquor l8 objectionable, the time of annealing will be much le'ss than would be is addedgtothepickle the amountof acid inthe batli, to clean the'metal ioundtabe reduced by about saving a considern wiehqo rnot add been pickling bath, neutralizes more or less of acid of the bath, whereby ,it becomes necessary to add slightlv greater amounts Anot er Y a relatively heavy coating or scale, a

necessary if the picklingwere performedwithout the acid concentrated li uor.

. When the acid-concentrated an] e liquor perinient that on account of the factthat the surface of the pickled ferrous metal articles is smoother when the acid-concentrated sulfite liquor is added, hence con-' siderably less tin or zinc is needed to coatrocess. For the purpose of the present invention, it is immaterial as to what these substances are, and we"do not limit the invention to any particular theog of why the acid-concentrated material" oujld' be better than the" neutralized concentrated material, but contentourselves with noting some of the specific advantages in :theuse of the acid-concentrated materialfi The uantity of the sulfite waste liquor to be added Wlll depend upon many factors and in general it may be stated'that enou h of the material should be added to su tantially increase the surface tension of the pickle liquor, foam will be roduced on thepickle liquor. In the following examples, roportions are stated forthe purpose of ustration and not as limiting the invention thereto.

Example 1. i

For pickling wrought iron pipes begin at llons of water, 80 pounds containing 100 and A pound of the acidof sulphuric aci concentrated sulfite liquor of about -'-32 results.

- Emwmfle 8. y Sheet steel "rolled plates on which the Be, gave good scale coating was relatively thin, were pickled in a bathcontainm 100 llons of water, 40 unds of hy hloric acid and poun of the acid concentrated sulfite liquor.

I Example 8. I For; pickling castings, having a rather thick coatingof rust, a-solution containing, in-"each' 100 'llons of water, about 100 pounds of hy ochloric acid and poundof acidaconcentrated sulfite liquor of about -32 36., gave saw u a For icklin iron rods to be 'su uentl I galvanized, th ese being madeof steez so that a relatively persistent a pickle bath was produced containing per 100 gallcns of water, 100 pounds of sulphuric acid and pound of the acidconcenti'ated sulfite liquor of about 30 B.

Ewample 5. For pickling steel rods to be subsequently cold drawn, a pickle bath was produce-Cl,

containing per 100 gallons of Water, 100 lbs. of 60 B6. sulphuric acid and 1 lbs. of the acid concentrated sulfite liquor cl 30-32 B6.

We claim:

1. A process of pickling ferrous metal articles, which comprises subjecting the same to the action of an acid pickling bath natures.

ADDISON F. HOFFMAN. WILLIAM M. PARKIN. 

